Blood pressure measuring apparatus, wrist watch type terminal having the same, and method of measuring blood pressure

ABSTRACT

Provided is a blood pressure measuring apparatus, a wrist watch type terminal, and a method of measuring blood pressure. The blood pressure measuring apparatus includes a light source that emits light onto a living body, a light receiver that receives light from the living body, and a signal processing device that calculates the blood pressure based on a detected signal received from the light receiver, wherein the signal processing device includes a subtractor that obtains a subtraction value by subtracting a moving average value of the detected signal in a second duration which is shorter than a first duration from a moving average value of the detection signal in the first duration, an extractor that extracts a feature point of a pulse wave based on the subtraction value, and a converter that converts a feature amount obtained based on the feature point to a blood pressure value.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from Japanese Patent Application No.2014-216125, filed on Oct. 23, 2014 in the Japanese IntellectualProperty Office, and Korean Patent Application No. 10-2015-0031116,filed on Mar. 5, 2015 in the Korean Intellectual Property Office, thedisclosures of which are incorporated herein in their entireties byreference.

BACKGROUND

1. Field

Apparatuses and methods consistent with exemplary embodiments relate toblood pressure measuring apparatuses, wrist watch type terminals havingthe same, and methods of measuring blood pressure.

2. Description of the Related Art

A blood pressure measuring apparatus may detect an amount of reflectionlight in a blood vessel as a photoelectric wave by radiating nearinfrared rays thereto. In particular, the blood pressure measuringapparatus may include a photoelectric sensor and a body movement sensor,and remove unnecessary frequency components of the photoelectric sensorand the body movement sensor. Blood pressure is calculated by using aratio of output values of the photoelectric sensor and a pressure sensoras a calibration value.

In the photoelectric blood pressure measuring apparatus, a pulse wave ismeasured in such a manner that a white noise or an alternating current(AC) component that is generated from a circuit is added to the pulsewave besides an AC component which is the intrinsic feature of the pulsewave. Accordingly, components besides the pulse wave of a living bodyare included as noise.

In particular, when a wrist watch type blood pressure measuringapparatus is used as a blood pressure measuring apparatus instead of acuff type blood pressure measuring apparatus, a mounting state of theblood pressure measuring apparatus is changed due to a movement of ameasuring subject or an external disturbance. Accordingly, the amount ofnoise increases, and thus, improvement of measurement precision isdifficult. Furthermore, a systolic blood pressure 2 (SBP2) may bedifficult to measure since the variation of a pulse wave is small.

SUMMARY

Exemplary embodiments address at least the above problems and/ordisadvantages and other disadvantages not described above. Also, theexemplary embodiments are not required to overcome the disadvantagesdescribed above, and may not overcome any of the problems describedabove.

One or more exemplary embodiments provide a blood pressure measuringapparatus that may precisely measure blood pressure, and method ofmeasuring the blood pressure.

According to an aspect of an exemplary embodiment, there is provided ablood pressure measuring apparatus including: a light receiverconfigured to receive light reflected from a living body; and a signalprocessing device that is configured to measure a blood pressure from apulse wave detected from the received light and include: a subtractorconfigured to obtain a subtraction value by subtracting a moving averagevalue of the detected pulse wave in a second duration which is shorterthan a first duration from a moving average value of the detected pulsewave in the first duration; an extractor configured to extract a featurepoint of the pulse wave based on the subtraction value; and a converterconfigured to convert the extracted feature amount obtained based on thefeature point to a blood pressure value.

The signal processing device may specify a cycle of the pulse wave basedon the subtraction value, the pulse wave having a plurality of cycles,may obtain a plurality of feature amounts by extracting the featurepoint respectively in each of the plurality of cycles of the pulse wave,and may calculate the blood pressure from the plurality of featureamounts.

The signal processing device may exclude one of the plurality of cyclesfrom which the feature point is not extracted due to noise from thecalculating of the blood pressure.

According to another aspect of an exemplary embodiment, a blood pressuremeasuring apparatus includes: a sensor including a light sourceconfigured to emit light onto a living body and a light receiverconfigured to receive light from the living body, the received lightcarrying a first detection signal and a second detection signal andbeing represented as a pulse wave; and a signal processing deviceconfigured to extract a first feature point and a second feature pointof the pulse wave based on the first detection signal and the seconddetection signal and convert a feature amount of the pulse wave to ablood pressure value based on the extracted first feature point and theextracted second feature point of the pulse wave, wherein the lightsource is further configured to output the first detection signal basedon light of a first wavelength range and the second detection signalbased on light of a second wavelength range that is shorter than thefirst wavelength range, and the signal processing device is furtherconfigured to extract the first feature point based on a systolic bloodpressure (SBP) that is based on the first detection signal in a firstduration of the pulse wave, extract the second feature point based onthe second detection signal in a second duration which is a durationdifferent from the first duration, and convert the feature amount intothe blood pressure value based on the first and second feature points.

The second feature point may include a maximum value and a minimum valueof a single pulse wave.

The light of the first wavelength range may be red light or infraredlight, and the light of the second wavelength range may be green light.

The light source alternately may emit the light of the first wavelengthrange during the first duration and the light of the second wavelengthrange during the second duration.

According to another aspect of an exemplary embodiment, a method ofmeasuring a blood pressure by using a blood pressure measuring apparatusthat includes a light source that emits light onto a living body, alight receiver that receives light from the living body, and a signalprocessing device that measures blood pressure based on a detectionsignal which is received from the light receiver and represented by apulse wave, the method including: obtaining a subtraction value bysubtracting a moving average value of the detection signal in a secondduration from a moving average value of the detection signal in a firstduration which is shorter than the second duration; extracting a featurepoint of the pulse wave based on the subtraction value; and converting afeature amount that is obtained based on the feature point to a bloodpressure value.

The first duration may be one cycle of a power source being used, andthe second duration may be 1 to 5 cycles of the pulse wave.

According to another aspect of an exemplary embodiment, a method ofmeasuring blood pressure by using a blood pressure measuring apparatusthat includes a sensor including a light source that emits light onto aliving body, and a light receiver that receives light from the livingbody, the received light carrying a first detection signal and a seconddetection signal and being represented as a pulse wave, and a signalprocessing device that extracts a first feature point and a secondfeature point of the pulse wave based on the first detection signal andthe second signal received from the sensor, and converts feature amountsbased on the first feature point and the second feature point to a bloodpressure value, the method includes: outputting the first detectionsignal based on light of a first wavelength range and the seconddetection signal based on light of a second wavelength range which isshorter than the first wavelength range; extracting the first featurepoint of the pulse wave in a first duration of a cycle of the pulse wavebased on an SBP that is obtained based on the first detection signal,and the second feature point based on the second detection signal in asecond duration that is different from the first duration in the cycle;and converting the feature amounts that are obtained based on the firstand second feature points to the blood pressure value.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and/or other aspects will be more apparent by describingcertain exemplary embodiments, with reference to the accompanyingdrawings, in which:

FIG. 1 is a block diagram of a configuration of a blood pressuremeasuring apparatus according to an exemplary embodiment;

FIG. 2 is a graph showing an example of a signal detected at a sensor ofa blood pressure measuring apparatus according to an exemplaryembodiment;

FIGS. 3A and 3B are graphs showing an example of a pulse wave from whichnoise is removed by using a digital filter and feature points of thepulse wave measured by a blood pressure measuring apparatus according toan exemplary embodiment;

FIGS. 4A and 4B are graphs showing linear regressions for converting afeature amount of a feature point extracted from a pulse wave that ismeasured by a blood pressure measuring apparatus to a blood pressureaccording to an exemplary embodiment;

FIG. 5 is a flow chart of a method of measuring a blood pressureaccording to an exemplary embodiment;

FIG. 6 is a block diagram of a configuration of a blood pressuremeasuring apparatus according to another exemplary embodiment; and

FIG. 7 is a graph for explaining a first duration and a second durationof one cycle of a pulse wave by a blood pressure measuring apparatusaccording to another exemplary embodiment.

DETAILED DESCRIPTION

Exemplary embodiments are described in greater detail below withreference to the accompanying drawings.

In the following description, like drawing reference numerals are usedfor like elements, even in different drawings. The matters defined inthe description, such as detailed construction and elements, areprovided to assist in a comprehensive understanding of the exemplaryembodiments. However, it is apparent that the exemplary embodiments canbe practiced without those specifically defined matters. Also,well-known functions or constructions are not described in detail sincethey would obscure the description with unnecessary detail.

Embodiment 1

A blood pressure measuring apparatus according to an exemplaryembodiment will be described with reference to FIG. 1. FIG. 1 is a blockdiagram of a configuration of a blood pressure measuring apparatus 1according to an exemplary embodiment. The blood pressure measuringapparatus 1 includes a sensor 10, an analogue front end (AFE) 20, asignal processing device 30, and a display 40. The blood pressuremeasuring apparatus 1 may be, for example, a measuring device installedon a wearable type terminal, and may be mounted on a wrist of an object(a human) by using a strap or a band. That is, the strap surroundsaround an arm, and thus, a blood pressure measuring state is achieved byusing the blood pressure measuring apparatus 1.

The sensor 10 includes a light source 11 and a light receiver 12. Thelight source 11 may be a light-emitting device, for example, alight-emitting diode (LED), and may emit green light, red light, orinfrared light. Light emitted from the light source 11 is radiated ontoa living body.

The light receiver 12 may be a light detector, for example, a chargecoupled device (CCD) or a complementary metal oxide semiconductor (CMOS)image sensor, and is disposed near the light source 11. The lightreceiver 12 receives light from a living body, and outputs a detectedsignal corresponding to the intensity of the received light to the AFE20. Accordingly, the sensor 10 is a photoelectric sensor that detects avolume pulse wave corresponding to a volume change of a blood vessel.

More specifically, when light emitted from the light source 11 isradiated onto a living body, the light is scattered at an epidermis, athick skin, a capillary vessel, a peripheral blood vessel, a fat, and anartery of the living body. The light receiver 12 detects the scatteredlight at various portions of the living body. A pulse flowing in theblood vessel moves at a constant time duration, and a feature movementis observed from the intensity (pulse wave) of the scattered lightobtained from the pulse. That is, the intensity of the scattered lightindicates a pulse wave. A living body index, such as a blood pressure,an oxygen content in blood, an augmentation index (AI) value, etc. maybe obtained by interpreting the pulse wave.

The light source 11 may emit red light or infrared light that readilypasses through a skin surface or a thick surface of a living body.Accordingly, the intensity of scattered light that is scattered in ablood vessel of a living body may be increased. The light receiver 12may be disposed to receive light passing through the living body. Atthis point, the light source 11 and the light receiver 12 are disposedto face each other with the living body therebetween.

The AFE 20 includes an amplifier 21, a noise removing filter 22, and ananalog digital converter (ADC) 23. The amplifier 21 amplifies a detectedsignal that is transmitted from the sensor 10. The noise removing filter22 is an analog filter and removes noise of the detected signal that isamplified at the amplifier 21. The noise removing filter 22 may be an LCfilter, such as a low pass filter or a high pass filter. The ADC 23converts the detected signal from which noise has been removed at thenoise removing filter 22 to a digital signal. Next, the ADC 23 outputsthe detected signal that has been converted to a digital signal to thesignal processing device 30. The ADC 23 outputs a digital value that issampled at a predetermined sampling duration as a detected signal.

The signal processing device 30 may be, for example, a microcomputer andmay include a central processing unit (CPU) 31, a memory 32, digitalfilter 33, and a power management module 34. The memory 32 stores apredetermined program. The CPU 31 reads and executes the program storedin the memory 32. In this manner, according to the detected signal atthe AFE 20, a systolic blood pressure (SBP) and a diastolic bloodpressure (DBP) may be measured. In order to measure a blood pressure, asdescribed below, the CPU 31 performs a processing for extracting afeature point and a processing for converting a feature amount to ablood pressure. Accordingly, as depicted in FIG. 1, the CPU 31 mayinclude an extractor 51 that extracts the feature point and a converter52 that converts the feature amount to the blood pressure. Also, thesignal processing device 30 may calculate a health index, for example,the AI value besides the blood pressure.

The power management module 34 controls power supplied to the sensor 10.For example, the power management module 34 allows the light source 11to emit light at a predetermined intensity by supplying a drivingcurrent to the light source 11. Also, the power management module 34 maycontrol the light source 11 to emit light at a predeterminedintermittent duration by controlling the current supplying time.

FIG. 2 is a graph showing a detected signal that is outputted from theAFE 20. As depicted in FIG. 2, a pulse wave according to a vascularpulsation is repeatedly appeared as a detected signal. Also, thedetected signal includes white noise or circuit noise that is generatedat an electronic circuit. The digital filter 33 performs a digitalprocessing that removes a noise component from the detected signal.Also, the CPU 31 measures a blood pressure in response to the detectedsignal from which the noise has been removed by the digital filter 33.

The digital filter 33 obtains a moving average with respect to thedetected signal. In order to obtain a moving average a(n) at anarbitrary time t(n), all data in periods of [t(n−m)˜t(n+m)] includingdata before and after the arbitrary time t(n) is added, and the addedvalue is divided by 2m+1. First, the digital filter 33 calculates amoving average of a first duration corresponding to a frequency of apower source as a first moving average. For example, a durationcorresponding to a 1 cycle (50 Hz or 60 Hz) of a commercial power sourceis determined as the first duration, and then, the digital filter 33obtains an average digital included in the first duration.

Next, the digital filter 33 calculates a second moving average from themoving average of a second duration which is longer than the firstduration. For example, the second duration is selected according to thepulse wave. A longer section than a single pulse is selected as thesecond duration. Here, as a practical example, a duration correspondingto one cycle of 0.47 Hz may be selected as the second duration. That is,the digital filter 33 obtains an average of digital value included in1/0.47 Hz. Since the second duration is longer than the first duration,the number of data included in the second duration is greater than thenumber of data included in the first duration. Accordingly, the secondmoving average has a smaller variation than the first moving average.

Also, the digital filter 33 is a subtractor that calculates asubtraction value which is calculated by subtracting the second movingaverage value from the first moving average value. FIG. 3A is a graphshowing an example of waveform of a subtraction value calculated fromthe first moving average value and the second moving average value. FIG.3A also shows an example of a subtraction value and a feature pointextracted from the subtraction value, and a magnified view of an idealpulse wave. FIG. 3B is a graph respectively showing different pulsewaves between a pulse wave obtained by red light and a pulse waveobtained from green light. Here, a subsequent computation process isperformed by using the result of the red light. An infrared light may beused instead of the red light.

The signal processing device 30, as depicted in FIGS. 3A and 3B, mayspecify a first cycle of a pulse wave from the time when the subtractionvalue is positive. In the following descriptions, a pulse wave of onecycle is referred to as a single pulse wave. The signal processingdevice 30 may set a time when the subtraction value is changed fromnegative to positive as a beginning point of the single pulse wave.

Next, the extractor 51 of the signal processing device 30 extracts afeature point of the single pulse wave according to the subtractionvalue. The signal processing device 30 extracts, for example, a firstmaximum value, a first minimum value, a second maximal value, a secondminimal value, and an inflection point as feature points at every singlepulse wave. The signal processing device 30 may calculate a value and atime of the feature point from the waveform of the subtraction value.For example, the signal processing device 30 calculates the featurepoint through calculating a pulse wave velocity by differentiating thepulse wave or calculating an acceleration pulse wave by differentiatingthe pulse wave twice. FIG. 3A shows an example of the feature pointextracted by the signal processing device 30.

In FIG. 3A, a first peak (maximum value) is a systolic peak and a secondpeak (maximal value) is a reflective peak in the first cycle. A minimalvalue after the second peak is a notch that indicates a boundary betweena systole and a diastole. A time from the beginning point of the cycleto the systolic peak is determined as an S. time. A time from thebeginning point of the cycle to a reflective peak is determined as an R.time. A time from the beginning point of the cycle to the notch isdetermined as a notch time. The signal processing device 30 extracts aminimum value as a feature point. In this manner, the signal processingdevice 30 calculates values and times of the feature points. Also, themaximum value and the minimum value may be calibrated based on thesubtraction value at the notch.

The signal processing device 30 calculates feature amounts from thevalues and times of a plurality of the feature points included in asingle pulse wave. The feature amounts denotes values for calculating anSBP and a DBP and are values derived from the values and times of thefeature points in the single pulse wave. The feature amounts may becalculated by an equation that is set in advance. The values of thefeature amounts vary according to the variation of a blood pressure, anduses values that greatly varies with respect to the blood pressure, andthus, the blood pressure may be precisely measured. Also, in the featurepoints, the subtraction value may be referred to as the feature amounts.Here, since both the SBP and the DBP are to be obtained, two equationsare needed.

Next, the converter 52 of the signal processing device 30 converts thefeature amounts to the blood pressure. The converter 52 converts thefeature amounts to the blood pressure by using a linear regression.Here, as shown in FIGS. 4A and 4B, in order to calculate the SBP BP_MAXand the DBP BP_MIN, two linear regressions are stored in the memory 32.The signal processing device 30 calculates the feature amount for theSBP and the feature amount for the DBP based on the single pulse wave.The signal processing device 30 calculates the SBP from a pre-determinedfeature amount by using the linear regression for the SBP. Also, thesignal processing device 30 calculates a DBP from another feature amountby using the linear regression for the DBP. In this manner, a bloodpressure is measured by using the blood pressure measuring apparatus 1.The extracted feature points and equations for calculating the featureamounts from the feature points may be optimized by using a well-knownmethod. That is, the feature points and the equations for preciselymeasuring the blood pressure are set.

The linear regression is set by using a plurality of measuring resultsthat are obtained in advance. That is, feature amounts are obtained byusing the blood pressure measuring apparatus 1 according to theexemplary Embodiment 1 with respect to a plurality of subjects, and atthe same time, a blood pressure is measured by using a cuff type bloodpressure measuring apparatus. Thus a data base of the feature amountscorresponding to the blood pressure value is constructed. Then, a linearregression is obtained by performing a regression analysis with respectto the recorded data base. The linear regression may be set according tosex and age, for example, males in their 20s, females in their 20s,males in their 30s, females in their 30s, etc. That is, after obtainingdata for sex and age, a data base may be constructed. The signalprocessing device 30 may convert the feature amounts to the bloodpressure by using not only a linear regression but also a regressioncurve that uses a polynomial expression, for example, a second-degreepolynomial expression or more.

Also, the signal processing device 30 may calculate a blood pressurebased on a plurality of pulse waves. For example, the signal processingdevice 30 may calculate feature amounts after extracting feature pointswith respect to n number (n is an integer more than 2) of pulse waves.In this manner, since the feature amounts are calculated for everysingle pulse wave, feature amounts of n numbers are calculated. Next,the signal processing device 30 converts the n feature amounts to an SBPor a DBP respectively by using the linear regression. In this manner,blood pressures of n numbers are calculated. An average of the n numbersof blood pressures may be regarded as a blood pressure. In this manner,when the feature amounts are calculated based on a plurality of pulsewaves, a measuring accuracy may be improved.

Also, a blood pressure may be obtained by excluding some of the nnumbers of blood pressures. For example, a blood pressure may beobtained from an average of n−2 numbers of blood pressures by excludingthe maximum and minimum blood pressures from the n numbers of bloodpressures. Accordingly, a blood pressure measuring accuracy may beimproved. Also, a pulse wave having big different values of featureamounts or feature points from other pulse waves may be excluded fromthe calculation of the blood pressure.

A single pulse wave (one cycle) from which feature points may not beextracted may be excluded from the calculation of the blood pressure.For example, when a maximal value or a minimal value that are requiredfor calculating feature amounts are buried in noise due to an effect ofthe noise, the feature amounts may not be calculated from thecorresponding cycle. Accordingly, the blood pressure may not beconverted from the single pulse wave (cycle) from which feature pointsmay not be extracted. In this manner, an accuracy of the blood pressuremay be improved.

In this manner, the signal processing device 30 determines the featurepoints, such as a first maximum value, a first minimum value, a secondmaximal value, and a second minimal value by determining rising orfalling characteristics of a pulse wave based on a subtraction value.Also, the signal processing device 30 may calculate the feature amountsfrom a plurality of feature points for every single pulse wave. Thesignal processing device 30 may convert the feature amounts to a bloodpressure by using a linear regression that is set in advance.

The display 40 includes a display monitor, such as a liquid crystaldisplay. The display 40 displays a waveform of a pulse wave that iscalculated by the signal processing device 30.

The blood pressure measuring apparatus 1 utilizes a subtraction valuebetween a moving average of a first duration and a moving average of asecond duration. In this way, the effect of diffusing noise besides anexternal disturbance light, vibration, and a pulse may be reduced.Accordingly, a precision of measuring a blood pressure may be improvedby appropriately extracting feature points. Also, a durationcorresponding to a frequency (50 Hz or 60 Hz) of a commercial powersource may be used as a first moving average value. In this manner,power source noise may be reduced.

Also, the digital filter 33 may reduce noise by digital processing thenoise. Accordingly, a blood pressure measuring apparatus may be simplymanufactured when compared to using an analog filter. For example, whennoise is removed by using the analog filter, it is necessary to design acircuit for the analog filter of a device where the analog filter isused. In the current exemplary embodiment, noise is removed throughprocessing a digital signal by a computer program, and thus, a bloodpressure measuring apparatus may have simple structure.

Moreover, the signal processing device 30 specifies 1 cycle (a singlepulse wave) of a pulse wave by using the subtraction value. That is, abeginning time of 1 cycle is specified at a time when the subtractionvalue is 0. In this way, a further appropriate feature amounts may beobtained. For example, since a time from the beginning time to a featurepoint may be precisely obtained, an appropriate feature amounts may beobtained. A first moving average value and a second moving average valueare obtained based on a detected signal of a single light receiver 12.In this manner, it is possible to appropriately estimate a noise level.Also, a further higher precision measurement is possible. If asubtraction value is obtained by frequently calculating a movingaverage, a high precision measurement is possible even though noise ischanged.

A method of measuring a blood pressure according to the exemplaryEmbodiment 1 is described with reference to FIG. 5, which shows a flowchart of a method of measuring a blood pressure.

First, the blood pressure measuring apparatus 1 is mounted on a part ofa measurement subject (living body), for example, a wrist, and lightemitted from a living body (wrist) is received by using the lightreceiver 12 (S1). The light receiver 12 performs a photoelectricconversion of a signal that indicates an intensity of the received lightand outputs the conversion result to the AFE 20.

Next, the AFE 20 processes a detected signal inputted from the sensor 10(S2). As described above, the amplifier 21 of the AFE 20 amplifies thedetected signal. The noise removing filter 22 filters the detectedsignal and removes noise. The ADC 23 performs an AD conversion of thedetected signal.

The digital filter 33 performs a digital filter processing with respectto the detected signal (S3). That is, noise is removed by obtaining asubtraction value between a first moving average value and a secondmoving average value. Also, a cycle may be specified by the subtractionvalue.

The signal processing device 30 extracts a feature point based on thesubtraction values (S4). For example, the signal processing device 30may extract the feature point by differentiating or differentiatingtwice a pulse wave that is appeared by the subtraction value. Here, thesignal processing device 30 extracts feature points on every singlepulse wave. That is, the signal processing device 30 calculates thefeature amounts on every single pulse wave based on values and times ofthe feature points (S5). That is, the signal processing device 30converts the values and times of the feature points to the featureamounts by using an equation that is set in advance. The feature amountsare not calculated from a pulse wave from which feature points are notextracted.

Next, the signal processing device 30 converts the feature amounts to ablood pressure by using a linear regression (S6). The signal processingdevice 30 calculates a SBP and a DBP. The display 40 displays theobtained blood pressure (S7). Through these processes, the effectsdescribed above may be obtained.

Also, when a bio information besides the blood pressure is to bemeasured, it is necessary to set an equation and a linear regression forobtaining a feature amount according to bio information of themeasurement subject (living body). For example, when blood oxygensaturation is measured, an equation is determined for calculating afeature amount from a feature point and a value of the feature point,etc. A data base is constructed by measuring the blood oxygen saturationwith respect to a plurality of measurement subjects in advance. Next, alinear regression is obtained according to the data base. In thismanner, blood oxygen saturation may be measured by using the bloodpressure measuring apparatus 1.

Embodiment 2

A blood pressure measuring apparatus according to another exemplaryembodiment will be described with reference to FIG. 6. FIG. 6 is a blockdiagram of a configuration of a blood pressure measuring apparatus. Inthe current exemplary embodiment, a feature point corresponding to aSBP2 is extracted. The SBP2 is a systolic rear blood pressure andcorresponds to the reflective peak of a systolic period of FIG. 3A. TheSBP2 is a feature point that exists before a notch after SBP1 of asingle pulse wave, and is used as an important index of bio-informationfrom which hardness (AI value) of a blood vessel may be derived.However, the SBP2 is difficult to extract since the variation of a pulsewave is small.

A configuration for extracting a feature point of the SBP2 will bedescribed. In the current exemplary embodiment, in order to extract thefeature point of the SBP2, two light sources, that is, a first lightsource 11 a and a second light source 11 b are installed on the sensor10. The basic configuration and processing of the blood pressuremeasuring apparatus 1 are the same as the exemplary embodiment, andthus, the description will not be repeated.

In the current exemplary embodiment, the sensor 10 includes the firstlight source 11 a and the second light source 11 b. The first lightsource 11 a emits light of a first wavelength range, for example,wavelength greater than 600 nm and below 1,100 nm. The second lightsource 11 b emits light of a second wavelength range that is shorterthan that of the first light source 11 a, for example, wavelengthgreater than 480 nm and below 560 nm. Light of the first wavelengthrange may be, for example, red light or infrared light and light of thesecond wavelength range may be green light. The first wavelength rangeand the second wavelength range may not be completely different fromeach other but some of them may overlap.

The power management module 34 allows the first light source 11 a andthe second light source 11 b to emit light at different times. Forexample, the power management module 34 allows the first light source 11a and the second light source 11 b to emit light alternately.Accordingly, the first light source 11 a and the second light source 11b intermittently emit light and the light-emitting cycles are the samebut the phases are different from each other.

The first light source 11 a and the second light source 11 b areadjacently disposed to each other. The first light source 11 a and thesecond light source 11 b radiate light toward almost the same part of aliving body. The light receiver 12 detects scattered light from the partof the living body on to which the light is radiated. The light receiver12 has sensitivity with respect to light of the first and secondwavelength ranges. That is, when the first light source 11 a emitsinfrared light, the light receiver 12 may detect light of wavelengthranges from infrared light to green light. When the first light source11 a emits red light, the light receiver 12 may detect light ofwavelength ranges from red light to green light.

When light is radiated onto a living body, obtained bio-information maybe different because the light reaching depths are different accordingto the wavelengths. For example, there is high possibility that greenlight is scattered near a depth of thick skin surface. However, redlight or infrared light is absorbed little in the living body and iseasily transmitted through the living body. When red light or infraredlight is used, the amount of scattered light is increased in an artery.Since a reaching depth of red light or infrared light is deep, muchinformation may be obtained. However, fat or peripheral blood vesselspresent in an epidermis or a thick skin besides the artery is small inamount, but affects as noise. This noise makes difficult to interpretthe scattered light, and interrupts the obtainment of a precisebio-information. However, since green light has a low light reachingdepth, noise due to scattered light by fat is little.

In the current exemplary embodiment, green light and red light orinfrared light having a wavelength longer than that of green light aredistinguishably used. More specifically, light (red light or infraredlight) of a first wavelength range is used in a first duration of asingle pulse wave, and light (green light) of a second wavelength rangeis used in a second duration. The sensor 10 controls to alternately emitlight of a first wavelength range and light of a second wavelengthrange. Accordingly, it is possible to perform a measurement at differentwavelengths with a simple configuration.

The emission timing of the first light source 11 a and the second lightsource 11 b will be described with reference to FIG. 7. FIG. 7 is agraph for explaining light emission timing at a pulse wave. A singlepulse wave may be divided into a first duration Tr and a second durationTg. The first duration Tr is an emission time for emitting red light orinfrared light. In the first duration Tr, the first light source 11 a isturned on and the second light source 11 b is turned off. The secondduration Tg is an emission time for emitting green light. In the secondduration Tg, the first light source 11 a is turned off and the secondlight source 11 b is turned on. The first duration Tr and the secondduration Tg are repeated. Light of the first wavelength range and lightof the second wavelength range are received by the light receiver 12.The ADC 23 converts the detected signal that is detected at apredetermined frequency to a digital value.

The second duration Tg includes a maximum value and a minimum value of asingle pulse wave. That is, the second duration Tg is a duration thatincludes a feature point (maximum value) based on a SBP1 and a featurepoint (minimum value) based on a DBP. In the second duration Tg, atiming before the minimum value is set as a start point and a timingafter the maximum value is set as an end point. In the first durationTr, the end timing of the second duration Tg is set as a start timing.The first duration Tr is a duration that is continued for apredetermined time from the end timing of the second duration Tg. An endtiming of the first duration Tr is the start timing of the secondduration Tg. The first duration Tr is a duration that includes a featurepoint based on a SBP2. In FIG. 7, the second duration Tg is longer thanthe first duration Tr. However, the second duration Tg may be shorterthan the first duration Tr.

The maximum value and minimum value of a single pulse wave may bereadily extracted. Accordingly, although green light that has weakintensity of light scattered from an artery is used, feature pointsbased on an SBP1 and a DBP may be readily extracted. However, thefeature point based on the SBP2 may be referred to as a minimal value, amaximal value, and an inflection point, and is difficult to extract.Accordingly, light of a first wavelength range is used for extractingthe feature point of the SBP2. In a light of the first wavelength range,the intensity of scattered light at an artery is high, and thus, afeature point of the SBP2 may be easily expressed as the maximal value.The signal processing device 30 relatively readily extracts a featurepoint corresponding to the SBP2.

In the current exemplary embodiment, in the first duration Tr thatincludes a feature point of an SBP2, light of a first wavelength rangeis detected. The signal processing device 30 extracts a feature point ofan SBP2 according to the light of a first wavelength range. In otherwords, the feature point of the SBP2 is extracted without using light ofthe second wavelength range. When light of the first wavelength range isused, the intensity of scattered light is increased, and thus, thefeature point of the SBP2 may be readily extracted. For example, inorder to extract the SBP2, it is unnecessary to differentiate a pulsewave twice or to interpret other data.

An example of processing method for extracting a feature point of anSBP2 will be described. Subtraction values from data neighboring eachother are obtained by using data of the first duration Tr in one cycleof a pulse wave. Next, a duration in which the subtraction values near 0appear is extracted by taking absolute values of the subtraction value.When counting the duration from the beginning of the cycle, it ispossible that a time corresponding to a second time within the duration,in which many subtraction values near 0 appear, may be regarded as theR. Time, and data near the time may be regarded as an SBP2. In thismanner, a feature amount of the SBP2 is obtained.

Also, the signal processing device 30 extracts a maximum value and aminimum value of a pulse wave based on light of a second wavelengthrange. A feature point based on an SBP1 and a feature point based on aDBP are extracted without using light of a first wavelength range. Theextraction of a maximum value and a minimum value of a pulse wave iseasy. Also, noise becomes small in green light. Accordingly, althoughgreen light that has a low intensity of scattered light at an artery isused, the signal processing device 30 may precisely extract the featurepoint.

Like in the exemplary Embodiment 1, the signal processing device 30calculates a blood pressure from the feature points. The signalprocessing device 30 obtains a feature amount from a plurality offeature points extracted from a single pulse wave. Next, the signalprocessing device 30 converts the feature amount to a blood pressure byusing a linear regression. The regression curve may be set by a database when light of a first wavelength range and light of a secondwavelength range are used. That is, after constructing the data base inwhich feature amounts and a pulse wave measurement correspond to eachother when light of a first wavelength range and light of a secondwavelength range are alternately radiated, and linear regression may beobtained by using this data base.

With respect to n cycles (n is an integer greater than 2) of a pulsewave, the signal processing device 30 calculates a feature amount onevery cycle. By these method, n numbers of blood pressures are obtained.The n numbers of blood pressure values are averaged by using n as aparameter. In this manner, a blood pressure may be precisely measured.

Also, as in the exemplary Embodiment 1, a pulse wave from which afeature point may not be extracted or pulse wave that has a featureamount largely different from other pulse waves may be excluded from thecalculation of a blood pressure. In the current exemplary embodiment, afeature point of an SBP2 is extracted by a detected signal that isdetected based on a light of a first wavelength range. Accordingly, thefeature point of the SBP2 may be precisely extracted. A pulse wave fromwhich a feature point of an SBP2 may not be extracted or a pulse wavethat has a feature point of the SBP2 largely different from other pulsewaves may be excluded from the calculation of a blood pressure.Accordingly, a blood pressure may be precisely measured in a short time.

Furthermore, the AI value may be obtained by using the feature point ofthe SBP2. For example, on a wrist, the AI value may be obtained from thefollowing equation.

AI=SBP2/SBP1(peak point of a pulse wave)×100

Regarding the setting of the first duration Tr and the second durationTg, the first duration Tr and the second duration Tg may beappropriately set after measuring a plurality of pulse waves. Forexample, after measuring a plurality of pulse waves of a measurementsubject, the signal processing device 30 may obtain a cycle of the pulsewave. Next, the signal processing device 30 may obtain information oftimes when a maximum value and a minimum value of a cycle are reached inevery pulse wave. Next, a duration that includes the maximum value andthe minimum value is set as a second duration, and a duration besidesthe second duration is set as a first duration.

In the current exemplary embodiment, light of a different wavelengthrange is used in a single pulse wave. That is, a single pulse wave isdivided into a first duration and a second duration, and lights ofdifferent wavelength ranges respectively are used during the firstduration and the second duration. In this manner, a feature point may beprecisely extracted. In particular, a feature point of an SBP2 may bereadily extracted. Accordingly, a blood pressure may be accuratelymeasured.

Furthermore, since the first light source 11 a and the second lightsource 11 b alternately emit light, the light receiver 12 outputs both afirst detected signal based on the first wavelength range and a seconddetected signal based on the second wavelength range. That is, thesingle light receiver 12 outputs the first detected signal based on thefirst wavelength range with respect to the first duration Tr and outputsthe second detected signal based on the second wavelength range withrespect to the second duration Tg. In this way, since the blood pressuremeasuring apparatus 1 includes a single light receiver 12 and a singleAFE 20, the configuration of the blood measuring apparatus may besimplified.

Also, in the above descriptions, the first and second light sources 11 aand 11 b having different light colors are installed. Accordingly, twolight receivers 12 may be installed. That is, a first light receiverthat receives light of a first wavelength range and a second lightreceiver that receives a second wavelength range may be installed in thesensor 10. In other words, a first light receiver that does not havesensitivity to the second wavelength range and a second light receiverthat does not have sensitivity to the first wavelength range may beinstalled. Also, one light source that emits lights of first and secondwavelength ranges and two light receivers respectively receive the firstand second wavelength ranges may be installed. In this case, a lightsource may be a white light source. Alternatively, two light sources andtwo light receivers may be installed. At this point, a first lightsource and a first light receiver that correspond to the firstwavelength range, and a second light source and a second light receiverthat correspond to the second wavelength range may be installed.

In the exemplary Embodiment 2, the digital process for removing noisefrom a detected signal by using the digital filter 33 shown in theexemplary Embodiment 1 may not be performed. That is, as described inthe exemplary Embodiment 1, a feature point may be extracted based on asubtraction value of two moving averages, and alternately, a featurepoint may be extracted based on a detected signal that is not digitalprocessed.

The blood pressure measuring apparatus 1 according to the exemplaryEmbodiments 1 and 2 may be mounted on a wearable terminal, such as awrist watch terminal. The blood pressure measuring apparatus 1 may bereferred to as a wrist watch terminal. Since the sensor 10 on the wristwatch terminal may include a wireless communication unit, other elements(for example, the signal processing device 30, the display 40, etc) maybe mounted on a smart phone. In this case, analog data or digital dataobtained by the wrist watch terminal is transmitted to the smart phonevia the wireless communication. The smart phone that receives the datamay perform a partial or an entire processing for measuring a bloodpressure.

In a blood pressure measuring apparatus according to an exemplaryembodiment and a method of measuring a blood pressure, noise may beremoved by using a subtraction value of moving average values, and thus,a high precision blood measurement is possible.

In a blood pressure measuring apparatus according to another exemplaryembodiment and a method of measuring a blood pressure, a feature pointof an SBP2 is calculated by using a first wavelength that is appropriatefor measuring the SBP2, and a maximum blood pressure is calculated bycalculating a feature point from which noise is reduced by using asecond wavelength which is longer than the first wavelength, and thus, ahigh precision blood measurement is possible.

While not restricted thereto, an exemplary embodiment can be embodied ascomputer-readable code on a computer-readable recording medium. Thecomputer-readable recording medium is any data storage device that canstore data that can be thereafter read by a computer system. Examples ofthe computer-readable recording medium include read-only memory (ROM),random-access memory (RAM), CD-ROMs, magnetic tapes, floppy disks, andoptical data storage devices. The computer-readable recording medium canalso be distributed over network-coupled computer systems so that thecomputer-readable code is stored and executed in a distributed fashion.Also, an exemplary embodiment may be written as a computer programtransmitted over a computer-readable transmission medium, such as acarrier wave, and received and implemented in general-use orspecial-purpose digital computers that execute the programs. Moreover,it is understood that in exemplary embodiments, one or more units of theabove-described apparatuses and devices can include circuitry, aprocessor, a microprocessor, etc., and may execute a computer programstored in a computer-readable medium.

The foregoing exemplary embodiments are merely exemplary and are not tobe construed as limiting. The present teaching can be readily applied toother types of apparatuses. Also, the description of the exemplaryembodiments is intended to be illustrative, and not to limit the scopeof the claims, and many alternatives, modifications, and variations willbe apparent to those skilled in the art.

What is claimed is:
 1. A blood pressure measuring apparatus comprising:a light receiver configured to receive light reflected from a livingbody; and a signal processing device configured to measure a bloodpressure from a pulse wave detected from the received light andcomprising: a subtractor configured to obtain a subtraction value bysubtracting a moving average value of the detected pulse wave in asecond duration which is shorter than a first duration from a movingaverage value of the detected pulse wave in the first duration; anextractor configured to extract a feature point of the pulse wave basedon the subtraction value; and a converter configured to convert theextracted feature amount obtained based on the feature point to a bloodpressure value.
 2. The blood pressure measuring apparatus of claim 1,wherein the signal processing device is further configured to specify acycle of the pulse wave based on the subtraction value, the pulse wavehaving a plurality of cycles, obtain a plurality of feature amounts byextracting the feature point respectively in each of the plurality ofcycles of the pulse wave, and calculate the blood pressure from theplurality of feature amounts.
 3. The blood pressure measuring apparatusof claim 2, wherein the signal processing device is further configuredto exclude one of the plurality of cycles from which the feature pointis not extracted due to noise, from the calculating of the bloodpressure.
 4. A blood pressure measuring apparatus comprising: a sensorcomprising a light source configured to emit light onto a living bodyand a light receiver configured to receive light from the living body,the received light carrying a first detection signal and a seconddetection signal and being represented as a pulse wave; and a signalprocessing device configured to extract a first feature point and asecond feature point of the pulse wave based on the first detectionsignal and the second detection signal and convert a feature amount ofthe pulse wave to a blood pressure value based on the extracted firstfeature point and the extracted second feature point of the pulse wave,wherein the light source is further configured to output the firstdetection signal based on light of a first wavelength range and thesecond detection signal based on light of a second wavelength range thatis shorter than the first wavelength range, and the signal processingdevice is further configured to extract the first feature point based ona systolic blood pressure (SBP) that is based on the first detectionsignal in a first duration of the pulse wave, extract the second featurepoint based on the second detection signal in a second duration which isa duration different from the first duration, and convert the featureamount into the blood pressure value based on the first and secondfeature points.
 5. The blood pressure measuring apparatus of claim 4,wherein the second feature point comprises a maximum value and a minimumvalue of the pulse wave.
 6. The blood pressure measuring apparatus ofclaim 4, wherein the light of the first wavelength range is red light orinfrared light, and the light of the second wavelength range is greenlight.
 7. The blood pressure measuring apparatus of claim 4, wherein thelight source is further configured to alternately emit the light of thefirst wavelength range during the first duration and the light of thesecond wavelength range during the second duration.
 8. A wrist watchterminal comprising the blood pressure measuring apparatus of claim 1.9. A method of measuring a blood pressure by using a blood pressuremeasuring apparatus that includes a light source that emits light onto aliving body, a light receiver that receives light from the living body,and a signal processing device that measures blood pressure based on adetection signal which is received from the light receiver andrepresented by a pulse wave, the method comprising: obtaining asubtraction value by subtracting a moving average value of the detectionsignal in a second duration from a moving average value of the detectionsignal in a first duration which is shorter than the second duration;extracting a feature point of the pulse wave based on the subtractionvalue; and converting a feature amount that is obtained based on thefeature point to a blood pressure value.
 10. The method of claim 9,wherein the first duration is one cycle of a power source being used,and the second duration is 1 to 5 cycles of the pulse wave.
 11. Themethod of claim 9, wherein the extracting the feature point comprisesspecifying a cycle of the pulse wave based on the subtraction value, thepulse wave having a plurality of cycles, obtaining a plurality offeature amounts by extracting the feature point respectively in each ofthe plurality of cycles of the pulse wave, and averaging the pluralityof feature amounts.
 12. The method of claim 11, wherein the extractingthe feature point comprises setting a timing when the subtraction valuechanges from negative to positive in the cycle of the pulse wave as astarting point of the cycle of pulse wave.
 13. The method of claim 11,wherein the extracting the feature point wave comprises extracting afirst maximum value, a first minimum value, a second maximal value, asecond minimal value, and an inflection point.
 14. The method of claim13, wherein the extracting of the feature point of the pulse wavecomprises excluding the cycle from which at least one of the firstmaximum value, the first minimum value, the second maximal value, thesecond minimal value, and the inflection point is not extracted due tonoise, from the converting to the blood pressure value.
 15. A method ofmeasuring blood pressure by using a blood pressure measuring apparatusthat includes a sensor including a light source that emits light onto aliving body, and a light receiver that receives light from the livingbody, the received light carrying a first detection signal and a seconddetection signal and being represented as a pulse wave, and a signalprocessing device that extracts a first feature point and a secondfeature point of the pulse wave based on the first detection signal andthe second signal received from the sensor, and converts feature amountsbased on the first feature point and the second feature point to a bloodpressure value, the method comprising: outputting the first detectionsignal based on light of a first wavelength range and the seconddetection signal based on light of a second wavelength range which isshorter than the first wavelength range; extracting the first featurepoint of the pulse wave in a first duration of a cycle of the pulse wavebased on a systolic blood pressure (SBP) that is obtained based on thefirst detection signal, extracting the second feature point based on thesecond detection signal in a second duration that is different from thefirst duration in the cycle; and converting amounts corresponding to thefirst and second feature points to the blood pressure value.
 16. Themethod of claim 15, wherein the second feature point comprises a maximumvalue and a minimum value of the pulse wave.
 17. The method of claim 15,wherein the light of the first wavelength range is red light or infraredlight, and the light of the second wavelength range is green light. 18.The method of claim 17, wherein the outputting the first detectionsignal comprises using the light of the first wavelength range duringthe first duration, using the light of the second wavelength rangeduring the second duration, and alternately using the light of the firstwavelength range and the light of the second wavelength range.
 19. Themethod of claim 15, wherein the extracting the second feature pointcomprises obtaining the feature amounts by extracting the second featurepoint respectively in each cycle of the pulse wave, and averaging thefeature amounts.
 20. The method of claim 19, wherein the extracting thesecond feature point comprises excluding a cycle from which at least oneof a maximal value and a minimal value is not extracted due to noise,from the converting to the blood pressure.